Found: a dependency chip ("inert unless drift.monitoring.enabled - hooks.enabled - hooks.drift_check.enabled") carried white-space:nowrap and measured 506px inside a 299px row at phone width, so it ran off the panel and was clipped. The page itself never scrolls sideways, so that text was simply unreachable. Fixed: .tag now takes max-width:100% and overflow-wrap:anywhere, guarded by a regression test in tests/test_prd_ui_export.py.

Re-measured after the fix, walking every element and comparing it against its nearest scroll container rather than the viewport: 0 clipped elements on all four tabs at all three widths with every group expanded. The page never scrolls sideways (scrollWidth == clientWidth) and the wide requests table scrolls inside its own .scroll container, which is the intended pattern.

Async writes: toggling journal.enabled off and back on wrote through to config.json both times with the navigation count staying at 1 - no reload - and aria-checked tracked the stored value each time. Toggles that need a fresh session carry a "new session" label.

Contrast: 16.10:1 body / 5.21:1 muted in light; 17.57:1 / 7.42:1 in dark - both above WCAG AA.